TiO2@MUF hybrid shell thermochromic phase change microcapsule and preparation method and application thereof

Abstract

The application provides a TiO2@MUF hybrid shell thermochromic phase change microcapsule and a preparation method and application thereof, and belongs to the technical field of functional energy storage materials. The microcapsule comprises a core layer and a shell layer, the core layer is a thermochromic phase change system composed of crystal violet lactone, bisphenol A and n-tetradecanol, the mass ratio of crystal violet lactone, bisphenol A and n-tetradecanol is 1:3-5:60-70, the shell layer is an organic-inorganic hybrid layer formed by stearic acid modified nano TiO2 and melamine-urea-formaldehyde resin, the mass proportion of stearic acid modified nano TiO2 in the shell layer is 0.10-0.25%, the phase change enthalpy of the microcapsule is greater than or equal to 110 J / g, the 24h light aging discoloration rate is less than or equal to 20%, and the light-heat conversion efficiency is greater than or equal to 88%. The microcapsule can be applied to temperature indication, anti-fake encryption, intelligent coating and functional fabric, and is especially suitable for solar energy utilization, electronic equipment heat dissipation and daily safety monitoring fields with high requirements for light resistance and energy storage stability.

Description

Technical Field

[0001] This application relates to a TiO2@MUF hybrid shell thermochromic phase change microcapsule, its preparation method and application, belonging to the field of functional energy storage materials technology. Background Technology

[0002] Solar energy, with its advantages of being clean, pollution-free, and having unlimited reserves, has become an important component of the future energy structure. However, the intermittency and volatility of solar energy significantly reduce its utilization efficiency—energy can be harvested through photothermal conversion under sunlight conditions, but a stable energy supply cannot be maintained during periods without sunlight. Therefore, coupling phase change energy storage technology with photothermal conversion technology has become a key approach to achieving stable and controllable utilization of solar energy.

[0003] Existing thermochromic phase change microcapsules have the following problems:

[0004] 1) Fluorane thermochromic dyes are extremely sensitive to ultraviolet radiation: thermochromic phase change microcapsules are prone to bond breakage or oxidative degradation, which leads to rapid fading and degradation of color-changing performance, severely limiting their application in outdoor or long-term light exposure environments.

[0005] 2) Difficulty in achieving both shell performance: Traditional organic shells (such as pure melamine-formaldehyde resin) have good flexibility but low thermal conductivity (usually <0.3 W / (m·K)), which affects the heat transfer efficiency after photothermal conversion. Pure inorganic shells (such as silicon dioxide and alumina) have high rigidity and excellent heat resistance, but they are brittle and prone to cracking, and cannot withstand the volume changes caused by multiple phase change cycles.

[0006] 3) Solid-liquid PCMs are prone to liquid leakage during phase change: This can lead to the loss of thermochromic phase change microcapsules and may also cause equipment corrosion or safety hazards.

[0007] In existing technologies, although some studies have attempted to improve microcapsule performance by using organic-inorganic hybrid shells, adding boron nitride and graphene to improve thermal conductivity, or introducing layered silicates to enhance barrier properties, these designs mostly focus on optimizing mechanical strength or thermal conductivity, without addressing the core issue of insufficient light resistance. At the same time, some preparation processes have drawbacks such as cumbersome procedures (e.g., multi-step modification, multiple centrifugation separations), large consumption of organic solvents (e.g., large-scale use of toluene and acetone), and harsh reaction conditions (e.g., high temperature and high pressure), resulting in high production costs and significant environmental pollution risks, making it difficult to meet the needs of large-scale industrial production. Summary of the Invention

[0008] In view of this, this application first provides a TiO2@MUF hybrid shell thermochromic phase change microcapsule to solve the problem of light resistance. The microcapsule has excellent photothermal conversion efficiency, phase change energy storage performance and mechanical stability. The fading rate after 24 h photoaging is less than 18.3%, the photothermal conversion efficiency is as high as 90.45%, the phase change enthalpy is not less than 120 J / g, and the phase change enthalpy retention rate is greater than 95%.

[0009] Specifically, this application is implemented through the following scheme:

[0010] A TiO2@MUF hybrid shell thermochromic phase change microcapsule includes a core layer and a shell layer. The core layer is a thermochromic phase change system composed of crystal violet lactone, bisphenol A (BPA), and n-tetradecanoic acid, with a mass ratio of crystal violet lactone (CVL), bisphenol A (BPA), and n-tetradecanoic acid of 1:3~5:60~70. The shell layer is an organic-inorganic hybrid layer formed by stearic acid modified nano-TiO2 (SA@TiO2) and melamine-urea-formaldehyde (MUF) resin, with the mass percentage of stearic acid modified nano-TiO2 in the shell layer being 0.10~0.25%.

[0011] The microcapsules with the above structure have a phase transition enthalpy ≥110 J / g, a 24-h photoaging fading rate ≤20%, and a photothermal conversion efficiency ≥88%.

[0012] The preferred mass ratio of crystal violet lactone, bisphenol A and n-tetradecyl alcohol is 1:3:60, and the mass percentage of stearic acid modified nano-TiO2 in the shell is 0.1~0.2%.

[0013] The average particle size of the microcapsules is 7~10 μm, and the particle size distribution is calculated using the span coefficient according to the formula, where D10, D50 and D90 are the particle sizes corresponding to 10%, 50% and 90% of the cumulative distribution, respectively.

[0014] Span≤1.0.

[0015] The TiO2@MUF hybrid shell thermochromic phase change microcapsules with the above characteristics were prepared by the following method:

[0016] Step 1: Stearic acid (SA), nano-TiO2 and anhydrous ethanol are mixed and stirred at 60~70 ℃. Stearic acid and nano-TiO2 are modified in anhydrous ethanol, and then centrifuged, washed and dried to obtain stearic acid modified nano-TiO2 (SA@TiO2).

[0017] Step 2: Crystal violet lactone (CVL), bisphenol A (BPA) and n-tetradecyl alcohol are mixed and stirred at 60-70 °C until clear. Deionized water is added and mixed. SA@TiO2 is added and ultrasonically emulsified to obtain Pickering emulsion.

[0018] Step 3: Mix urea, melamine and formaldehyde, adjust the pH to 8-9, stir at 60-70 ℃, and cool with ice water to obtain MUF prepolymer;

[0019] Step 4: Adjust the pH of the Pickering emulsion to 4-5, add MUF prepolymer dropwise, react at 50-60 °C, filter, wash, and freeze-dry to obtain TiO2@MUF hybrid shell thermochromic phase change microcapsules.

[0020] Preferred:

[0021] In step one,

[0022] The mass ratio of stearic acid to nano-TiO2 is 0.2~0.7:2.

[0023] The stearic acid-modified nano-TiO2 has a water contact angle of 80~90°, a grafting rate of 4~6%, and an absorption intensity ≥0.8 in the 200~400 nm ultraviolet range (1 cm cuvette, concentration 0.1 g / L).

[0024] When the mass ratio of SA to nano-TiO2 is 0.4:2, stirring at 70 ℃ is the optimal modification condition. At this temperature, the water contact angle of SA@TiO2 is 88.65° and the grafting rate is 5.32%.

[0025] In step two,

[0026] The mass ratio of crystal violet lactone (CVL), bisphenol A (BPA), and n-tetradecyl alcohol is 1:3:60.

[0027] The ultrasound power is 30~40 W, and the duration is 10~15 min.

[0028] The average particle size of the Pickering emulsion is 7.23~10.22 μm.

[0029] The volume ratio of the clarified solution to the added deionized water is 3~4:2~3.

[0030] In step three,

[0031] The formaldehyde used is a 37 wt% formaldehyde solution.

[0032] The mixing ratio of urea, melamine and 37 wt% formaldehyde solution is 9.1 g: 5.6 g: 37 mL.

[0033] In step four, the dropping rate of the MUF prepolymer is 1~2 mL / min.

[0034] The above scheme first forms a stable thermochromic emulsion through Pickering emulsification, then polymerizes it with MUF prepolymer under acidic conditions to construct an organic-inorganic hybrid shell for microcapsules. SA@TiO2 acts as a Pickering emulsifier to stabilize the oil-water interface and enhances lightfastness through UV shielding. MUF resin forms a dense cross-linked structure through condensation polymerization, fixing SA@TiO2 and inhibiting core material leakage. The shell and core layers work together to endow the prepared microcapsules with excellent lightfastness and stable energy storage. Without losing its color-changing ability, lightfastness and thermal conversion efficiency are improved, and the fading rate is reduced. The preparation process is green, controllable, and easily scalable.

[0035] The application of the above-mentioned TiO2@MUF hybrid shell thermochromic phase change microcapsules in functional coated fabrics is as follows:

[0036] S1, microcapsules, deionized water and waterborne polyurethane are mixed to obtain a coating liquid.

[0037] The preferred mixing ratio of the microcapsules, deionized water, and waterborne polyurethane is 0.5~1g:10mL:5~10g.

[0038] S2, the cotton fabric is dipped in the coating liquid and dried to obtain the functional coated fabric.

[0039] The cotton fabric is preferably a pure cotton fabric.

[0040] The dipping time is 20-30 minutes.

[0041] The drying process refers to treatment at 60~70℃ for 10~15 minutes.

[0042] The functional coated fabric obtained by the above method has a 10-hour light aging fading rate of ≤40% and a microcapsule shedding rate of ≤10% after 5 washes.

[0043] The aforementioned TiO2@MUF hybrid shell thermochromic phase change microcapsules can also be used in temperature indication, anti-counterfeiting encryption, or smart coatings, and are especially suitable for solar energy utilization, electronic device heat dissipation, and daily safety monitoring fields that have high requirements for light resistance and energy storage stability.

[0044] The beneficial effects of this invention can be summarized as follows:

[0045] (1) Improved shell density and environmental resistance: The present invention uses the cross-linked network structure formed by in-situ polymerization of MUF resin to form a dual protection of "physical barrier-chemical cross-linking" with TiO2 nanoparticles, which reduces the core material leakage rate, significantly improves the strength and stability of the product, broadens its application range in industrial production and material improvement, and avoids the breakage of microcapsules during processing or use.

[0046] (2) Improved light resistance: The UV shielding effect of TiO2 reduces the photo-aging degradation of the MUF shell, with a fading rate of only 18.2%. This significantly improves the stability of the microcapsules and broadens their application range.

[0047] (3) Improved photothermal conversion efficiency: The photothermal conversion efficiency is 90.45%, the phase change enthalpy is 120 J / g, and the phase change enthalpy retention rate is >95%. It can couple phase change energy storage technology with photothermal conversion technology to become a stable material for realizing stable and controllable utilization of solar energy.

[0048] The microcapsules provided by this invention solve the problems of poor light resistance and limited functionality of existing products. The preparation process is simple and controllable, suitable for industrial production, and can be widely used in temperature monitoring, anti-counterfeiting packaging and smart textiles, with significant economic and social benefits. Attached Figure Description

[0049] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application.

[0050] Figure 1 This is a SEM image of the microcapsules in Example 1 on a 10 μm scale.

[0051] Figure 2 This is a SEM image of the microcapsules in Example 1 on a 1μm scale.

[0052] Figure 3 To characterize the performance of stearic acid-modified nano-TiO2, part (a) shows the effect of SA content on the water contact angle, part (b) shows the FTIR spectra of TiO2, SA@TiO2 and SA, part (c) shows the thermogravimetric analysis comparison of TiO2, SA@TiO2 and SA, and part (d) shows the UV-Vis spectra of TiO2 and SA@TiO2.

[0053] Figure 4To characterize the phase transition behavior of TiO2@MUF, part (a) of the figure shows the DSC heating curves of TiO2@MUF and TiO2@MUF-1 to TiO2@MUF-4, part (b) shows the DSC cooling curves of TiO2@MUF and TiO2@MUF-1 to TiO2@MUF-4, part (c) shows the phase transition temperature histogram of thermochromic phase change materials (TC-PCMs) and TiO2@MUF series samples, and part (d) shows the phase transition enthalpy histogram of TiO2@MUF and TiO2@MUF series samples.

[0054] Figure 5 shows the heat storage and heat release characteristics of TC@MF with different TC-PCM contents. Part (a) in the figure shows the experimental conditions under simulated sunlight, and part (b) shows the heat storage and heat release characteristic curves of TC@MF with different TC-PCM contents.

[0055] Figure 6 To demonstrate the optical stability and durability of the microcapsules obtained in Example 1 during repeated thermochromic processes, part (a) of the figure shows the color development and fading curves, part (b) shows the change of the CIE Lab colorimetric parameter L* value in the color development and fading states, part (c) shows the change of the CIE Lab colorimetric parameter a* value in the color development and fading states, and part (d) shows the change of the CIE Lab colorimetric parameter b* value in the color development and fading states.

[0056] Figure 7 To illustrate the temperature indication effect of this application, part (a) of the figure shows the time response effect of the microcapsules of this application, part (b) shows the natural cooling effect of the plaster doll containing the microcapsules of this application, and part (c) shows the effect of the microcapsules of this application as a temperature indicator bar. Detailed Implementation

[0057] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the technical solutions in the embodiments of this application will be further described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit the technical solutions of this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without creative effort are within the scope of protection of this application.

[0058] Example 1

[0059] This embodiment provides a TiO2@MUF hybrid shell thermochromic phase change microcapsule, which is prepared using the following process:

[0060] Step 1, Preparation of stearic acid modified nano-TiO2 (SA@TiO2): Weigh 0.4g of stearic acid, 2g of nano-TiO2, and 20g of anhydrous ethanol according to the mass ratio and add them to the reaction vessel; mechanically stir at 70 ℃ for 3 h to allow the stearic acid to fully react with the TiO2 surface; after the reaction is completed, the product is centrifuged and washed 3 times with anhydrous ethanol, and dried to obtain SA@TiO2 powder with a stearic acid grafting rate of approximately 5.32%.

[0061] Step 2, Preparation of thermochromic Pickering emulsion: Weigh each core material component according to the mass ratio of CVL:BPA:n-tetradecyl alcohol = 3:1:60 and add them to a container; stir vigorously at 70 ℃ for 60 min until a clear and transparent core material solution is formed; mix the core material solution with deionized water at a volume ratio of 4:3, add 0.1% SA@TiO2 emulsifier by mass; use a 40W cell disruptor for ultrasonic emulsification for 15 min to obtain a stable thermochromic Pickering emulsion.

[0062] Step 3, Preparation of MUF shell prepolymer: Weigh 9.1 g of urea, 5.6 g of melamine, and 37 mL of 37 wt.% formaldehyde solution, and add 20 mL of deionized water; adjust the pH of the system to 8.5 with triethanolamine, and stir at 70 ℃ for 30 min until the solution is clear and transparent; immediately place the solution in ice water to cool, and obtain the MUF shell prepolymer for later use.

[0063] Step 4, Preparation of TiO2@MUF hybrid shell thermochromic phase change microcapsules: The Pickering emulsion obtained in Step 2 was transferred into a three-necked flask, and the pH was adjusted to 4.5 with citric acid; the MUF prepolymer solution prepared in Step 3 was slowly added dropwise at a rate of 1 mL / min; after the addition was complete, the mixture was reacted at 55 °C for 2 h to allow the MUF prepolymer to crosslink and solidify on the surface of the emulsion droplets; after the reaction was completed, the product was filtered, washed with deionized water, and freeze-dried to obtain TiO2@MUF hybrid shell thermochromic phase change microcapsules, denoted as TiO2@MUF-1.

[0064] The structure and properties of the obtained microcapsules were identified:

[0065] Combination Figure 1 It can be seen that the average particle size is about 10 μm, the surface is dense and regularly spherical, and it has a core-shell encapsulation structure.

[0066] Combination Figure 2 It can be seen that the modified particles are embedded in the shell.

[0067] As shown in Figure 3(a), unmodified TiO2 exhibits strong hydrophilicity due to its abundant surface hydroxyl groups, resulting in a water contact angle of only about 20°, making it difficult to effectively fix at the interface and causing the emulsion to easily break down. Surface modification by introducing long-chain stearic acid significantly improves its wettability. When the amount of SA is 25 wt%, the contact angle increases to 88.65°, approaching the ideal 90°, achieving the balanced wettability required for stable emulsion formation. Therefore, this study selected the sample prepared under these conditions as SA@TiO2 for subsequent structural and performance characterization.

[0068] Figure 3 (b) shows the FTIR spectra of TiO2, SA@TiO2, and stearic acid (SA). The spectrum is at 3421 cm⁻¹. -1 A hydroxyl stretching vibration peak appears at 1637 cm⁻¹. -1 The peak at this location is the hydroxyl bending vibration peak, 400–600 cm⁻¹. -1 The characteristic peaks in the region correspond to the vibrations of the Ti–O–Ti bonds, reflecting the hydroxyl groups and framework structure characteristics of the TiO2 surface. SA peaks are observed at 2918 and 2850 cm⁻¹. -1 and 1702 cm -1 Typical alkyl and carbonyl absorption peaks were observed at [insert locations here]. In contrast, SA@TiO2 showed absorption peaks at 2918, 2850, and 1467 cm⁻¹. -1 The new peak, and 1702 cm -1 and 941 cm -1 The peaks for polar groups significantly decreased, indicating that the polar portion of stearic acid had participated in the bonding. Meanwhile, the peaks at 1535 and 1405 cm⁻¹... -1 The carboxylate peak at that location splits, and Δν is calculated to be 130 cm⁻¹. -1 The results are consistent with the bridging coordination characteristics, indicating that stearic acid forms Ti–O–C bonds with the TiO2 surface through the carboxyl group, thereby improving the hydrophobicity of the particles and the stability of the interface.

[0069] Figure 3 Thermogravimetric analysis in (c) further confirmed the chemical bonding. Pure TiO2 showed only slight weight loss (adsorption of water) at 100 °C, while SA decomposed rapidly in the range of 200–300 °C. In contrast, SA@TiO2 showed a weight loss peak at 250–450 °C, requiring higher energy for destruction, confirming that stearic acid was chemically grafted onto the TiO2 surface in a stable manner, with a grafting amount of approximately 5.32%.

[0070] Figure 3The UV-Vis spectral analysis (d) shows that both TiO2 and SA@TiO2 maintain strong UV absorption in the 200–400 nm range, while absorption in the >500 nm visible region is close to zero, indicating that the modification does not affect their UV shielding performance. Combined with the high refractive index and scattering effect of TiO2, SA@TiO2 can still effectively block UV radiation and maintain its light transmittance.

[0071] Example 2

[0072] To investigate the phase transition behavior of TiO2@MUF samples with different formulations, the other settings in this embodiment are the same as in Example 1, except that in step two, SA@TiO2 emulsifier is added in the following quantities: 0 (i.e., the core layer without a shell, denoted as TC-PCMs), 0.05%, 0.15% (corresponding microcapsules denoted as TiO2@MUF-2), 0.20% (corresponding microcapsules denoted as TiO2@MUF-3), 0.25% (corresponding microcapsules denoted as TiO2@MUF-4), 0.30%, and 0.35% respectively.

[0073] Compared to the product without SA@TiO2 emulsifier (SA@TiO2 emulsifier addition amount is 0), Example 1 exhibits better lightfastness and energy storage stability, solving the problems of poor lightfastness and limited functionality in existing products. With increasing SA@TiO2 emulsifier addition, interface coverage becomes more complete, emulsion stability gradually increases, and the shell structure becomes denser. Correspondingly, energy storage, barrier, lightfastness, and photothermal properties all show an increasing trend, albeit at relatively low levels. When the SA@TiO2 emulsifier addition is controlled at around 0.20% (such as 0.10-0.25% mentioned above), especially at 0.20%, interface coverage is saturated, particle distribution is uniform, the hybrid shell density is optimal, and all properties reach their peak values, representing the optimal dosage for multifunctionality. When the amount of SA@TiO2 emulsifier reaches 0.25%, if the amount of SA@TiO2 emulsifier is continued to be increased, the microcapsule forming process will be in an excessive state. At this time, particle agglomeration will occur, resulting in a decrease in the uniformity of the emulsion template, local structural defects in the shell, and a slight decline in performance, but it is still better than Example 1.

[0074] The heat flow curves of the heating and cooling processes in Examples 1 and 2 were tested using differential scanning calorimetry (DSC). Results Figure 4 As shown:

[0075] from Figure 4 As shown in heating curve (a), each sample exhibits a distinct endothermic peak in the range of 50–60 °C, corresponding to the melting process of the thermochromic core material, with a peak temperature T. m The small differences between different formulations indicate that the coating process has a limited impact on the phase transition temperature. Figure 4The cooling curves in (b) show that each sample exhibits an exothermic peak in the range of approximately 30–50 °C, corresponding to the crystallization temperature T. C and recrystallization temperature T R There is a certain degree of overcooling (T) R –T C ).

[0076] and Figure 4 The statistical results of phase transition temperature (c) show that the T of the sample after microencapsulation treatment is: m T C With T R All of them are slightly offset from the original TiO2@MUF, which is related to the spatial confinement effect of the shell on the movement of the molecular chain segments of the core material. Figure 4 The statistical results of the latent heat of phase change in (d) show that the latent heat of endothermic reaction of the microcapsule sample Hd is... m and exothermic and latent heat H c Compared to TC-PCMs, all showed a decrease, which is due to the increased proportion of microcapsule shell components in the total mass, diluting the content of effective phase change substances. Furthermore, with increasing SA@TiO2 emulsifier addition, H... m With H c The trend of recovery is related to the improved thermal conductivity after optimization of shell structure density, core material coverage, and TiO2 addition.

[0077] Comprehensive analysis shows that the TiO2@MUF sample maintains a high latent heat of phase transition while still possessing a phase transition temperature range close to that of the original core material, and the coating process does not significantly weaken its heat storage capacity. This indicates that by rationally controlling the shell composition and the proportion of TiO2 added, excellent thermal storage performance can be achieved while ensuring mechanical stability and optical functions.

[0078] exist Figure 5 Under simulated sunlight conditions (a) in section (a), the applicant studied the heat storage and release characteristics of TC@MUFs with different shell (TC-PCM) contents. Figure 5As shown in (b), all TC@MUF (TiO2@MUF-1 to TiO2@MUF-4) series samples exhibited a distinct temperature plateau between 45 and 52 °C during the heating process. This is attributed to the absorption of latent heat by the core material cetyl alcohol during the phase transition, resulting in a delay in temperature rise. A similar hysteresis phenomenon also occurred during the cooling process, with two temperature plateaus visible on the time-temperature curve, corresponding to the release of latent heat during crystallization. This phenomenon is consistent with the results of the DSC cooling curve, further verifying the existence of phase transition behavior. With the increase of TC-PCM content, the heating rate of the samples gradually increased, which is related to the deepening of color and enhanced light absorption effect after the increase of thermochromic dye content. It is worth noting that the thermochromic transition temperature range is basically consistent with the phase transition temperature range of cetyl alcohol, allowing the color change of the microcapsules to directly reflect their melting or crystallization state. It is evident that TC@MUF possesses the ability to regulate temperature and manage heat through latent heat absorption and release.

[0079] To systematically evaluate the optical stability and durability of the samples during repeated thermochromic processes, the samples were subjected to 100 isothermal heating / cooling cycles between 25 ℃ and 65 ℃, and their reflectance spectra and CIE Lab colorimetric parameters were measured in both the colored and faded states. Taking TiO2@MUF-1 as an example, as shown in Figure 6(a), the colored state (red curve) exhibits a stable and strong characteristic absorption peak near 520 nm, corresponding to the selective absorption of visible light by the blue color center; the faded state (gray curve) shows almost no significant absorption in the entire visible light region, reflecting the complete fading of color. Notably, the spectral profiles and peak intensities of the two states before and after cycling are almost identical, indicating that the material maintains excellent spectral response consistency under multiple thermal cycles.

[0080] Figure 6(b) to Figure 6 The CIE Lab colorimetric parameter analysis in (d) further confirms this conclusion: the differences between L* (brightness), a* (red-green axis), and b* (yellow-blue axis) in the color-developing and fading states are highly reproducible throughout the entire cycle, with no significant drift or attenuation, indicating that the color saturation, hue, and brightness of the samples are highly reversible. This stability can be attributed to the effective physical isolation and structural protection of the thermochromic core material by the microcapsule shell, avoiding optical performance degradation caused by molecular degradation, migration, or leakage during repeated heating / cooling. In summary, all TC@MUF series samples provided in this application still exhibit excellent thermochromic reversibility and optical retention after 100 thermal cycles, demonstrating their application potential in long-term service environments.

[0081] Application Example 1

[0082] This application example uses TiO2@MUF-1 prepared in Example 1 as the object, and applies it to functionalized coated fabrics. The process is as follows:

[0083] A coating solution was prepared by mixing 0.5 g microcapsules, 10 mL deionized water and 10 g waterborne polyurethane (WPU). The coating solution was then applied to pure cotton fabric for 20 min and dried at 60 ℃ for 15 min to obtain the functionalized coated fabric.

[0084] The performance of the obtained functionalized coated fabrics was evaluated:

[0085] The functionalized coated fabric has a 10-hour light aging fading rate of ≤40% and a microcapsule shedding rate of ≤10% after 5 washes.

[0086] Application Example 2

[0087] This application example uses the TiO2@MUF hybrid shell thermochromic phase change microcapsules prepared in Example 1 as the object, and applies them to temperature indication. The process is as follows:

[0088] The time-response properties of the microcapsules were observed after mixing them with waterborne polyurethane (WPU), and the results are as follows: Figure 7 As shown in (a) in the figure: the freshly prepared mixed solution is colorless, turns slightly light blue after 5s, and turns distinctly blue after 12s, which confirms that the microcapsules of this application can respond quickly to temperature changes with very intuitive color changes.

[0089] like Figure 7 As shown in (b): When a WPU plaster doll coated with microcapsules was placed at 70°C and then allowed to cool naturally to room temperature, the doll gradually changed from white to blue.

[0090] and Figure 7 In (c), microcapsules are used as a temperature indicator coating on a water cup (microcapsules can be directly coated on the surface of the water cup, or microcapsules can be evenly dispersed with WPU and then coated on the surface of the water cup as a coating). When filled with 100°C water, it appears white. As the temperature decreases, the color gradually changes from white to light blue (e.g., at 50°C), and finally appears dark blue at room temperature (25°C).

[0091] The above results indicate that this application, as a coating, can achieve a fast and reversible color response.

[0092] Comparative Example 1

[0093] Taking CN112473581A as a comparative example 1, it adopts a double-shell structure of "resin inner layer + silicon dioxide outer layer", which only realizes the binary function of "magnetic response + phase change energy storage". Its preparation requires two-step shell formation and its application is limited to magnetically controlled directional energy storage scenarios.

[0094] This application addresses the critical bottleneck of poor lightfastness of thermochromic dyes by innovatively designing a TiO2@MUF organic-inorganic hybrid shell structure. Stearic acid-modified TiO2 (SA@TiO2) is used as a Pickering emulsifier to anchor the oil-water interface, achieving one-step shell formation through synergistic curing with MUF resin. This structure not only combines thermochromism (temperature indication), high-efficiency photothermal conversion (90.45%), high latent heat storage (phase change enthalpy 120 J / g), and excellent lightfastness (18.3% accelerated photoaging fading rate in 24 hours) in a quaternary functional coupling, but also features a lower leakage rate (2.3%) and more uniform microcapsule morphology. Its applications cover multiple fields such as temperature indication, photothermal-energy storage integration, and anti-counterfeiting encryption. Furthermore, the preparation process is simpler, and the utilization rate of functional components is higher, overcoming the limitations of single-function positioning and application in the references. This aligns better with the development trend of "multifunctional, long-life, and easy-to-apply" intelligent functional materials.

[0095] Comparative Example 2

[0096] Taking CN118360033A as a comparative example 2, it adopts a traditional multi-layer shell or single organic / inorganic shell design, and its preparation requires multi-step coating or complex dispersion processes. Its function is limited to energy storage or simple color change, and it lacks the synergistic effect of photothermal-energy storage-color change.

[0097] This application aims to address the core pain points of thermochromic materials, namely easy fading and limited functionality. It innovatively designs an organic-inorganic hybrid shell structure composed of SA-modified TiO2 and MUF resin. Through Pickering emulsification, a one-step shell formation is achieved, enabling TiO2 to simultaneously perform the triple functions of emulsification stabilization, UV shielding, and photothermal enhancement. This not only achieves thermochromism (temperature visualization), high-efficiency photothermal conversion (90.45%), and high latent heat storage (phase change enthalpy 120°C), but also realizes high latent heat energy storage. The quaternary functional coupling of J / g and excellent light stability (18.3% fading rate after 24h photoaging) also has a more uniform microcapsule morphology (particle size 7.23μm, Span=0.61) and a lower thermal cycling leakage rate (2.3%). The preparation process is simpler and the utilization rate of functional components is higher. The application scenarios cover multiple fields such as temperature indication, integrated photothermal energy storage, and anti-counterfeiting encryption. It breaks through the limitations of Comparative Example 2, which has a single function, complicated preparation, and insufficient long-term service stability. It is more in line with the core requirements of smart materials: "multifunctional synergy, long life and easy application".

[0098] Comparative Example 3

[0099] Taking CN118022642A as a comparative example 3, it also adopts a traditional single organic shell or simple composite shell structure, relies on conventional emulsifiers to achieve encapsulation, and its function is limited to temperature response and basic energy storage. It also suffers from problems such as complex preparation process, uneven microcapsule particle size distribution, and insufficient long-term service stability.

[0100] This application aims to overcome the bottleneck in the practical application of thermochromic materials. It innovatively designs an organic-inorganic hybrid shell structure composed of stearic acid-modified TiO2 (SA@TiO2) and MUF resin. By modifying the TiO2 contact angle with SA, efficient Pickering emulsification is achieved, completing the shell coating in one step. This allows TiO2 to simultaneously perform the triple functions of emulsification stabilization, UV shielding, and photothermal enhancement. This results in thermochromism (temperature visualization), high photothermal conversion efficiency (90.45%), high latent heat storage (phase change enthalpy 120 J / g), and excellent light stability (24h). The quaternary functional coupling with a photoaging fading rate of 18.3% also has a more uniform microcapsule morphology (particle size 7.23μm, Span=0.61) and a lower thermal cycling leakage rate (2.3%). The preparation process is simpler and the utilization rate of functional components is higher. The application scenarios cover multiple fields such as temperature indication, photothermal-energy storage integration, and anti-counterfeiting encryption. It overcomes the shortcomings of single function, lack of light resistance and limited practical application in literature, and is more in line with the development needs of "multifunctional synergy, long life and easy industrialization" of smart functional materials.

[0101] The above-described embodiments are merely illustrative of several feasible implementations of the present invention, and their descriptions are relatively specific and detailed. However, they should not be construed as limiting the scope of the present invention, nor are the embodiments intended to limit the scope of protection in the claims of the present invention. For those skilled in the art, various modifications and improvements can be made without departing from the concept of the present invention. All equivalent implementations or changes that do not depart from the present invention should be included in the technology of the present invention.

Claims

1. A TiO2@MUF hybrid shell thermochromic phase change microcapsule, characterized in that: The device comprises a core layer and a shell layer. The core layer is a thermochromic phase transition system composed of crystal violet lactone, bisphenol A, and n-tetradecanoic acid, with a mass ratio of crystal violet lactone, bisphenol A, and n-tetradecanoic acid of 1:3~5:60~70. The shell layer is an organic-inorganic hybrid layer formed by stearic acid-modified nano-TiO2 and melamine-urea-formaldehyde resin, with a mass percentage of stearic acid-modified nano-TiO2 in the shell layer of 0.10~0.25%. The water contact angle of the stearic acid-modified nano-TiO2 is 80~90°, the grafting rate is 4~6%, and the absorption intensity in the 200~400 nm ultraviolet range, at a 1 cm cuvette and a concentration of 0.1 g / L is ≥0.

8. The preparation method of the TiO2@MUF hybrid shell thermochromic phase change microcapsules is as follows: Step 1: Stearic acid, nano-TiO2 and anhydrous ethanol are mixed and stirred at 60~70 ℃, centrifuged, washed and dried to obtain stearic acid modified nano-TiO2. The mass ratio of stearic acid to nano-TiO2 is 0.2~0.7:

2. Step 2: Bisphenol A, crystal violet lactone and n-tetradecyl alcohol are mixed and stirred at 60~70 ℃ until clear. Deionized water is added and mixed. Stearic acid modified nano TiO2 is added and ultrasonically emulsified to obtain Pickering emulsion. The average particle size of Pickering emulsion is 7.23~10.22 μm. Step 3: Mix urea, melamine and formaldehyde, adjust the pH to 8-9, stir at 60-70 ℃, and then cool with ice water to obtain MUF prepolymer; Step 4: Adjust the pH of the Pickering emulsion to 4-5, add MUF prepolymer dropwise, react at 50-60 °C, filter, wash, and freeze-dry to obtain TiO2@MUF hybrid shell thermochromic phase change microcapsules; The TiO2@MUF hybrid shell thermochromic phase change microcapsules have a phase change enthalpy ≥110 J / g, a 24 h photoaging fading rate ≤20%, and a photothermal conversion efficiency ≥88%.

2. The TiO2@MUF hybrid shell thermochromic phase change microcapsule according to claim 1, characterized in that: The mass ratio of crystal violet lactone, bisphenol A and n-tetradecyl alcohol is 1:3:60, and the mass percentage of stearic acid modified nano-TiO2 in the shell is 0.1~0.2%.

3. The TiO2@MUF hybrid shell thermochromic phase change microcapsule according to claim 1, characterized in that: The average particle size of the microcapsules is 7~10 μm.

4. The TiO2@MUF hybrid shell thermochromic phase change microcapsule according to claim 1, characterized in that: In step two, the volume ratio of the clarified solution to the added deionized water is 3~4:2~3.

5. The application of the TiO2@MUF hybrid shell thermochromic phase change microcapsule of claim 1 in functional coated fabrics, characterized in that: Microcapsules, deionized water, and waterborne polyurethane are mixed to obtain a coating liquid. Cotton fabric is then coated with the coating liquid and dried to obtain a functional coated fabric. The functional coated fabric has a 10-hour light aging fading rate ≤40% and a microcapsule shedding rate ≤10% after 5 water washes.

6. The application of the TiO2@MUF hybrid shell thermochromic phase change microcapsule of claim 1 in temperature indicating components, anti-counterfeiting encryption facilities, or smart coatings.

Images